1. Field of the Invention
The present invention relates to and includes an apparatus for use as a fracture absorption layer, an apparatus for use as an electrochemical device, and methods of manufacturing the same. The apparatuses and methods of the present invention may be of particular use in the manufacture of thin-film, lightweight, flexible or conformable, electrochemical devices such as batteries, and arrays of such devices. The present invention may provide many advantages including stunting fractures in a first electrochemical layer from propagating in a second electrochemical layer.
2. Description of the Art
During electrochemical charging of electrochemical devices, such as, for example, lithium-free and lithium-ion, solid-state, thin-film, secondary battery configurations, the lithium anode may be formed as an entirely new layer (as in a lithium-free configuration) or the lithium anode may expand up to 400% of its original, as fabricated thickness (as in the lithium-ion configuration). The electrochemical device may contain a metallic lithium anode which may be configured wither with an initially lithium-accepting cathode, such as V2O5, or an initially lithium-donating cathode, such as LiCoO2. In the former case, the metallic lithium anode will contract significantly during the initial electrochemical step (discharge) whereas in the latter case the metallic lithium anode will expand significantly during the initial electrochemical step (charge). These volume changes may create stress points and planes that may be managed only with difficulty, prior to the present invention. These volume changes, which may be referred to herein as “breathing,” may reverse during each battery half-cycle. Consequently, a single-layer thin-film electrolyte (for example, lithium phosphorus oxynitride (Lipon)) may, unfortunately, be bulk fractured as a net amount of lithium atoms is transferred from the positive cathode to the negative anode (this process may be referred to as “battery charge”) and as a net amount of lithium atoms is transferred from the negative anode to the positive cathode (this process may be referred to as “battery discharge”).
This problem may be aggravated in the aforementioned, highly stressed lithium-free and lithium-ion battery configurations, but may also occur in lithium batteries (such as those in which a metallic lithium anode is already present in the as-fabricated state). Thus, all lithium-based, solid-state, thin-film, secondary battery configurations (lithium, lithium-free, and lithium-ion) may suffer from the same stress-creating effect, the “breathing” of such batteries during electrochemical cycling.
Fracture of the thin-film electrolyte may occur through its bulk. Such bulk fracturing of this electrolyte, even when it presents a crack width of only several angstroms across, can result in undesirably high battery current leakage. Indeed, high battery current leakage is generally associated with or considered a complete battery failure. As a result, only low operation yields and poor reliability with lithium-free and lithium-ion configurations had been obtained prior to the present invention. The operation yield may be defined as the fraction of batteries (or other electrochemical devices) in a fabrication batch that does not develop an internal current leak during the first step (otherwise known as the activation of the battery), which is a charge for batteries configured with a lithium-donating cathode and is a discharge for batteries configured with a lithium-accepting cathode. This first step is, in each case, the time at which the stress levels are the highest. Although for lithium and lithium ion batteries both cathode types can be used, lithium-free batteries can be configured only with lithium-donating cathodes otherwise electroplating of the metallic lithium anode can not be accomplished.
In contrast, the fabrication yield may be defined as the fraction of non-leaking batteries (or other electrochemical devices) in a fabrication batch prior to the initial step (charge or discharge depending on the nature of the cathode). Previously, the fabrication yields of all lithium-based, solid-state, thin-film, secondary battery configurations (lithium, lithium-free, and lithium-ion) were comparable to each other and approximately 95%. However, only the lithium batteries had a 95% operation yield. The lithium-ion batteries had a maximum operation yield of about 75% and the lithium-free batteries had a maximum operation yield of about 50%. Additionally, many non-leaking lithium-free and lithium-ion thin-film batteries developed leaks during later cycles. Thus, the yield of non-leaking lithium-free and lithium-ion batteries after 1000 cycles was less than 10%.
Presently a need exists to provide this battery technology on thin flexible foils and polymers. Also, lithium-free and lithium-ion configurations (configurations in which there is not a deposited lithium anode) are becoming increasingly valuable as a way of eliminating the difficulties and hazards of processing a metal lithium anode. In particular, there is a need to provide these configurations on flexible substances.
Unfortunately, an integral and critical component of these desired cells, the lithium phosphorus oxynitride (Lipon) electrolyte, is traditionally fabricated as a single-layer, glassy, thin-film ceramic. Consequently, it has been problematic to make batteries that survive conformable strains associated with flexing, bending, or wrapping. These externally induced strains may lead to bulk fractures (fractures that extend through the entire electrolyte layer, either immediately or eventually upon subsequent battery operation in later cycles) of this single layer ceramic electrolyte. As a result the battery may leak electrical current or fail.
Likewise, lithium-free and lithium-ion configurations may experience internal contraction and expansion stresses and strains. These stresses and strains may be associated with the creation of an in-situ electroplated, interposed lithium anode layer between the electrolyte and the metallic anode current collector during cycling of lithium-free batteries. Similarly, the strong expansion and contraction of the lithium-ion anode in lithium-ion batteries may also cause bulk fractures. These internal stresses and strains may produce bulk fractures with the same result as those fractures that are externally induced. These fractures in the traditionally single layer ceramic electrolyte may similarly lead to battery leakage or failure. Thus, both electrical cycling and mechanical deformation may have the same detrimental effect on thin-film batteries fabricated with a single layer of ceramic electrolyte such as Lipon.
Traditionally, rigid ceramic, glass, and silicon planar wafers have been provided as substrates for solid-state thin-film battery fabrication. More recently, a need has arisen to provide solid-state thin-film batteries on flexible substrates such as metal foils and polymer films. Achieving batteries on such substrates, as, for example, addressed by the present invention, may provide the advantages of reducing the substrate thickness and weight, thereby enabling energy storage device incorporation into tighter, conformable, and flexible space configurations.
Attempts at creating certain thin-film batteries have been published. For example, U.S. Pat. Nos. 6,218,049; 5,567,210; 5,445,906; 5,338,625; 6,168,884; and WO 98/47,196 describe methods for fabricating thin-film deposited lithium-based batteries. Similarly, U.S. Pat. No. 5,512,147 describes a thin-film electrolyte, lithium phosphorus oxynitride or Lipon, that can be employed in solid-state thin-film lithium-based batteries.
U.S. Pat. No. 5,314,765 describes a multilayer of electrolyte materials consisting of an organic polymer containing inorganic lithium salt bulk electrolyte adjoining a thin film of the aforementioned Lipon electrolyte material. similarly WO 99/43,034describes a multilayer of electrolyte materials consisting of a bulk layer of Li2S4 “catholyte” adjoining a thin film of the aforementioned Lipon electrolyte material. However, unlike the present invention, these inventions utilize Lipon as an additional chemical separator from a lithium anode to an organic polymer electrolyte, rather than to serve in any form of fracture absorbing capacity.
U.S. Pat. Nos. 5,455,106; 5,545,435; and 5,558,907 describe combinations of multi-layer refractory ceramic coatings interposed with very thin fugitive carbon coatings in ceramic composites for the stunting of fractures within this multi-layer interfacial system. U.S. Pat. No. 4,837,230 describes refractory and carbon layers interposed with ceramic matrix layer interfaces as applied to ceramic reinforcement fabric for crack propagation inhibiting and flexural strength increase. WO 97/21,538 and U.S. Pat. No. 5,948,196 disclose a multi-layer ceramic film interface on fibers for crack stunting within the interfacial layers.
An alternative mechanism that has been proposed in the use of thin-film interlayers in composites to eliminate bulk, brittle, composite fracture is the provision of a poorly adhered or chemically debonded, thin-film slip layer for the fiber pullout required in high strength composites. U.S. Pat. No. 4,980,202 describes certain fracture toughness associated with the application of a carbon coating on reinforcing fibers in ceramic composite systems for a sliding interfacial layer which enables the fibers to strain, thereby increasing the strength of and eliminating brittle fracturing of the composite. U.S. Pat. No. 5,682,594 describes a variety of thin-film interlayer compositions for similar application in discontinuous fiber or whisker reinforced composite systems. British Patent No. GB 2,236,540 uses thick boron nitride interlayers for fiber pullout and crack blunting in ceramic composites. These latter patents describe examples of the use of thin films to change interfacial properties. In these instances the desired properties are connected with lubricity or reduced adhesion related to linear shearing during fiber pullout. In contrast, the interfacial properties of the multi-layer electrolyte of the present invention may be adapted to maintain good ionic conductivity with adjoining layers, and therefore good adhesion, in order to facilitate battery function, while eliminating the propagation of fractures.
Multi-layers of thin films may also be applied in a non-analogous art as hard coatings to cutting tools and dies as well as gears and other mechanical parts for extended lifetime of the coated device. Examples of multi-layer systems for wear coatings are as follows: U.S. Pat. No. 5,268,216 discloses the application of layers of MoS2, a dry thin-film lubricant, interposed with very thin metallic layers to alter the growth mechanism of multiple interlayers and provide for containment of cracks within the multi-layer system; Korean Patent KR 9,612,317 describes crack prevention on cutting tools by a multi-layer of metal bonded thin films in conjunction with ceramic wear resistant layers; U.S. patent application Ser. No. 2001/016273 describes many ultra-thin multi-layers of alternating composition ceramic layers for abrasive wear resistance; and WO 00/08,234 discloses a multi-layer composite coating of refractory layers of varied composition as micro-crack barriers.